Question 930 Deck Safety

The correct answer is D) completely closed. When the bypass valve of a self-contained breathing apparatus (SCBA) is opened, the mainline valve should be completely closed. This is because the bypass valve is used to provide an alternative air supply in case of a malfunction or failure of the main regulator. With the bypass valve open, the air flow is diverted from the mainline, and closing the mainline valve prevents the uncontrolled release of air from the SCBA cylinder. The other options are incorrect because: A) immediately disconnecting the mainline valve is not necessary and could be dangerous; B) completely opening the mainline valve would not be appropriate when the bypass valve is in use; and C) pinching the mainline valve to check the air flow would not be the proper response in this situation.